LONDON (Reuters) - Four men have been arrested in connection with the ambush killings in Ivory Coast of seven U.N. peacekeepers on its border with Liberia, Ivory Coast President Alassane Ouattara said on Friday. An adviser to Ouattara said the four had been arrested in Liberia and would be extradited to Ivory Coast to stand trial. The seven United Nations peacekeepers, all from Niger, were killed on June 8 when their patrol came under fire near the town of Tai, close to the porous border, in what Ivorian authorities said was a cross-border raid. ...